Dr. C. E. Shannon proposed a theory that improved performance could be obtained from data transmission systems by encoding, transmitting the data, and decoding using an error correcting decoder. Work has proceeded on this theory for more than 25 years and a number of systems developed. The most recent is the convolutional encoder and Viterbi decoder. There are other techniques which may be used and this invention relates to a Multiple Decoding System which encodes and decodes either a digital bit stream in segments up to eleven data bits by adding five code bits; or encodes and decodes the data on a word by word basis. This coding and decoding system is not like either block codes or convolutional codes.
The Viterbi decoder with rate 1/3 coding and using antipodal transmission has six states of ambiguity and has a coding loss of 4.8 db; the coding loss of the Multiple Decoding System is less than 11/2 db. Superior performance, while theoretically possible with the convolutional encoding and Viterbi decoding has not been demonstrated with respect to the Multiple Decoding System. The severe coding loss for convolutional encoding with a rate of 1/3 code provides a definite problem not present with the Multiple Decoding System. The performance of each system is approximately equal. The low coding loss and no tendency to propogate errors provides a margin of superiority for the Multiple Decoding System. This disclosure explains the code, method of encoding, Parity I and Parity II decoding, Sequential decoding and then selecting a single output from the two methods for the final Multiple Decoder System output.
Parity decoding is a technique for decoding encoded signals which have been encoded using a unique method for generating a plurality of check bits. One received bit error per data word can be corrected from the received data while two bit error per data word received can be correctly decoded for the majority of words using the code characteristics and probability theory based upon the received signal magnitude for each bit received. Sequential decoding is a completely different method of decoding. In this method, the bits received are ranked by magnitude and the bits of high rank are used first in decoding. The bits with the lowest rank are not used and these have the greatest probitility of error. Because they are not used, most words are correctly decoded. Multiple decoding uses a combination of both Parity and Sequential decoding.